1. Field of the Invention
The present invention relates to a semiconductor substrate called an SOI substrate or the like and a method of producing the same.
2. Related Background Art
There are known methods for producing the SOI substrate having a single-crystal semiconductor thin film in such a manner that an Si wafer as a first base is bonded to another Si wafer as a second base with an insulating layer being interposed therebetween and a part of the first base on the back surface side is removed to make the single-crystal semiconductor thin film transferred onto the second base.
Particularly, the methods utilizing a porous layer, described in Japanese Patent Publication No. 2608351 and U.S. Pat. No. 5,371,037, are excellent methods to obtain an SOI substrate with good quality.
Further, U.S. Pat. No. 5,374,564 also describes a method of producing an SOI substrate making use of a layer with microbubbles (porous layer) formed by execution of ion implantation of hydrogen ions and a heat treatment.
The inventor prepared SOI substrates according to the description of the above patents. The inventor then made an MOS transistor using these SOI substrates and found that in application of this transistor to a high-frequency circuit, more improvement was required in high-frequency characteristics of the transistor and the circuit.